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 Cgs and Cgs vs Vgs 

Last post Sun, Mar 16 2014 1:08 PM by anhnha. 5 replies.
Started by anhnha 14 Mar 2014 07:13 PM. Topic has 5 replies and 545 views
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  • Fri, Mar 14 2014 7:13 PM

    • anhnha
    • Not Ranked
    • Joined on Fri, Mar 14 2014
    • Posts 11
    • Points 145
    Cgs and Cgs vs Vgs Reply

     Hi.
    I set up this circuit for simulation Cgs and Cgs as Vgs changes.

     

    Below are the curves Cgs and Cgs vs Vgs.
    (please see it in the second post. The forum doesn't allow to post two images in a single post)

    I have some questions, hope you can help.

    1. Why Cgs and Cgs are negative?
    2. Why Cgs and Csg are not equal?
    Thanks.


    • Post Points: 5
  • Fri, Mar 14 2014 7:14 PM

    • anhnha
    • Not Ranked
    • Joined on Fri, Mar 14 2014
    • Posts 11
    • Points 145
    Re: Cgs and Cgs vs Vgs Reply

     Here are the curves Cgs and Cgs vs Vgs:

     


    • Post Points: 20
  • Sun, Mar 16 2014 12:34 AM

    Re: Cgs and Cgs vs Vgs Reply

    If this is a bsim3v3 or a bsim4 model, they are not strictly capacitances - they are partial derivatives:

    cgs (F)           dQg_dVs
    csg (F)           dQs_dVg

    Many years ago (over 15) spectre changed to use the native operating point parameters in the model rather than the traditional "SPICE" meanings of cgs etc, and I wrote a note describing this change (which published by a colleague at the time as this solution). This explains a bit more why they are negative and that the traditional "cgs" capacitance value would be found by taking -csg as reported by spectre.

    Regards,

    Andrew.

    • Post Points: 20
  • Sun, Mar 16 2014 2:18 AM

    • anhnha
    • Not Ranked
    • Joined on Fri, Mar 14 2014
    • Posts 11
    • Points 145
    Re: Cgs and Cgs vs Vgs Reply

    Hi.

    Thanks a lot for the explanation. Could you attach the solution? The link doesn't work for me.  

    • Post Points: 20
  • Sun, Mar 16 2014 3:22 AM

    Re: Cgs and Cgs vs Vgs Reply

    Try this instead. It contains the same information. However, in general you should be able to access Cadence Online Support if you're a customer on maintenance - if you are from a university, there is a mechanism via whoever is running the university programme at your university (it depends on the region you're from precisely how that works).

    Andrew.

    • Post Points: 20
  • Sun, Mar 16 2014 1:08 PM

    • anhnha
    • Not Ranked
    • Joined on Fri, Mar 14 2014
    • Posts 11
    • Points 145
    Re: Cgs and Cgs vs Vgs Reply

     Thank you.

    • Post Points: 5
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Started by anhnha at 14 Mar 2014 07:13 PM. Topic has 5 replies.